assert_width

Ensures that when value of a specified expression is TRUE, it remains TRUE for a minimum number of clock cycles and transitions from TRUE no later than a maximum number of clock cycles.


	Parameters: severity_level min_cks max_cks property_type msg coverage_level	Class: n-cycle assertion

Syntax

Parameters


	severity_level	Severity of the failure. Default: ‘OVL_ERROR.
	min_cks	Minimum number of clock edges test_expr must remain TRUE once it is sampled TRUE. The special case where min_cks is 0 turns off minimum checking (i.e., test_expr can transition from TRUE in the next clock cycle). Default: 1 (i.e., same as 0).
	max_cks	Maximum number of clock edges test_expr can remain TRUE once it is sampled TRUE. The special case where max_cks is 0 turns off maximum checking (i.e., test_expr can remain TRUE for any number of cycles). Default: 1 (i.e., test_expr must transition from TRUE in the next clock cycle).
	property_type	Property type. Default: ‘OVL_ASSERT.
	msg	Error message printed when assertion fails. Default: “VIOLATION”.
	coverage_level	Coverage level. Default: ‘OVL_COVER_ALL.

Ports


	clk		Clock event for the assertion. The checker samples on the rising edge of the clock.
	test_expr		Expression that should evaluate to TRUE for at least min_cks cycles and at most max_cks cycles after it is sampled TRUE.

Description

The assert_width assertion checker checks the single-bit expression test_expr at each rising edge of clk. If the value of test_expr is TRUE, the checker performs the following steps:

1. Unless it is disabled by setting min_cks to 0, a minimum check is initiated. The check evaluates test_expr at each subsequent rising edge of clk. If its value is not TRUE, the minimum check fails. Otherwise, after min_cks -1 cycles transpire, the minimum check terminates.

2. Unless it is disabled by setting max_cks to 0, a maximum check is initiated. The check evaluates test_expr at each subsequent rising edge of clk. If its value does not transition from TRUE by the time max_cks cycles transpire (from the start of checking), the maximum check fails.

3. The checker returns to checking test_expr in the next cycle. In particular if test_expr is TRUE, a new set of checks is initiated.

Assertion Checks


	MIN_CHECK	The value of test_expr was held TRUE for less than min_cks cycles.
	MAX_CHECK	The value of test_expr was held TRUE for more than max_cks cycles.
	min_cks > max_cks	The min_cks parameter is greater than the max_cks parameter (and max_cks >0). Unless the violation is fatal, either the minimum or maximum check will fail.

Cover Points


	test_expr_asserts	A check was initiated (i.e., test_expr was sampled TRUE).
	test_expr_asserted_for_min_cks	The expression test_expr was held TRUE for exactly min_cks cycles (min_cks > 0).
	test_expr_asserted_for_max_cks	The expression test_expr was held TRUE for exactly max_cks cycles (max_cks > 0).

assert_width #(
	‘OVL_ERROR, 2, 3, ‘OVL_ASSERT, “Error: invalid request”, ‘OVL_COVER_ALL)		// severity_level // min_cks // max_cks // property_type // msg // coverage_level
	valid_request (
		clk, reset_n, req == 1);	// clock // reset // test_expr